Detecting the presence of a specific miroorganism is useful as a diagnostic tool as well as for other reasons. In the past mircroorganisms have been detected by growing a colony of them on a suitable medium and then examining the colony microscopically. This method is slow and expensive. In general it must be conducted in a laboratory and it takes several days which makes it unsatisfactory for quick diagnosis, for example, in a physician's office.
Techniques have been developed to detect the presence of specific microorganisms by detecting the presence of enzymes produced by those microorganisms rather than looking for the microorganisms themselves. This technique generally uses a synthetic substrate that reacts in the presence of a microorganism's enzyme to produce a compound that is identified by color or by fluorescence in ultraviolet radiation (UV). U.S. Pat. No. 4,388,233 issued to Bissell et al. is representative of the process employing this technique.
The technique of the Bissell et al patent in general employs a compound having an A portion of molecule fragment and a B portion of molecule fragment connected by a hydrolyzable peptide bond. The A portion is specific to the enzyme to be detected in that the presence of that enzyme will cause the peptide bond to be hydrolyzed to thereby produce two molecules, one of which is made from the A fragment and one of which is made from the B fragment. The B fragment of the molecule has a colorimetric or fluorescent quality that permits detection of the enzyme by observing a color change or fluorescence. Specifically, if the detection compound changes color it is because the microorganism's enzyme was present and the B compound was formed with its characteristic color or fluorescing characteristic. The A portion or fragment of the molecule is enzyme-specific, that is, the A portion or fragment of the molecule will cause it to hydrolyze in the presence of the enzyme of the particular microorganism being detected but will prevent hydrolysis of the peptide link or bond by enzymes other than the one to be detected.
Problems encountered with this method for detecting microorganisms are that sharp, unequivocal results are sometimes difficult to obtain. Known colorimetric and fluorescent tests frequently produce equivocal results in which a color shift must be compared with a standard which frequently requires a subjective determination or fluorescense and is difficult to distinguish from the background or difficult to observe because the visible radiation resulting from fluorescense is too close to the blue spectrum as well as being weak. In many such tests different analysts will reach different conclusions regarding a color change or fluorescence.